Membrane Permeability Flashcards

1
Q

What molecules can pass freely across the plasma membrane?

A

Small uncharged polar molecules (water, urea, glycerol)

Hydrophobic molecules and gases (o2, CO2, n2, benzene)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

If Gibbs free energy △G is positive the diffusion is _________

A

Active - change in free energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

If Gibbs free energy △G is negative the diffusion is _________

A

Passive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is active transport?

A

Allows movement of ions/molecules against their concentration or electrical gradient (unfavourable)
Energy required indirectly or directly from ATP hydrolysis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Which cells have high energy expenditure on active transport?

A

Nerves
Muscle
Erythrocytes
Enterocytes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the general intracellular and extracellular Na concentrations?

A

Outside 145 mM

Inside 12 mM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the general intracellular and extracellular K concentrations?

A

Outside 4 mM

Inside 155 mM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the general intracellular and extracellular Cl concentrations?

A

Outside 123 mM

Inside 4 mM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the general intracellular and extracellular Ca concentrations?

A

Outside 1-2 mM

Inside 100 nM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is uniport?

A

Only one type of molecule transported at a time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is cotransport?

A

More than one ion/molecules transported at a time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is symport?

A

Cotransport in the same direction

E.g. Na/Glucose cotransported in small intestine and kidney

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is antiport?

A

Cotransport in opposite directions

E.g. NCX.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the function of the Na/K ATPase?

A

Active transporter present in every cell
Transports 3Na out of cell and 2K into cell per ATP molecule hydrolysed

Acts to maintain cellular concentrations of Na and K (form the gradients)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What channels are responsible for resting membrane potential (~-70mV) ?

A

K diffusion through K+ channels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the main function of the K/Na ATPase?

A

Form sodium and potassium gradients which are necessary for electrical excitability

Also derived secondary active transport (cotransport)

17
Q

How does the Na/k ATPase regulate ph?

A

Sodium gradient generated by Na/k ATPase is used to exchange H+ ions out of the cell (1:1 exchange)

18
Q

What is high intracellular toxic to cells?

A

Causes precipitation of phosphate (ossification) and Pi can’t be recycled

19
Q

What is the role of mitochondrial Ca uniporters?

A

At high cytoplasmic calcium, operate as a buffer to take calcium into mitochondria (facilitated diffusion), induces caspase pathway which induces apoptosis of the cell (cell death at high [Ca2+]

20
Q

In control of pH which two exchangers are important in lowering acid (H+ leaves)?

A
  • Na/H exchanger (NHX) - one Na in, one H out

- Na dependent Cl-/HCO3- exchanger - one Na in , 1 H out, 1 HCO3 in, 1 Cl out

21
Q

What does electroneutral mean?

A

The number of positive/negative charges leaving is equal to the the charge entering

E.g. Na/H exchanger

22
Q

What is the Na/H exchanger activated and inhibited by ?

A

Activated by growth factors

Inhibited by amiloride (K+ sparing diuretic)

23
Q

In control of pH which exchanger is important in lowering base inside cell (HCO3- leaves)?

A
  • Cl/HCO3- anion exchanger - one HCO3- out, 1 Cl in

Important in peripheral circulation

24
Q

What molecules are important in cell volume regulation?

A

Water follows osmotically active ions such as Na, K, Cl (6 molecules of water move across membrane per one ion) and organic osmolytes (such as amino acids) into/ out of cell causes shrinking or swelling

25
What mechanisms resist cell swelling (remove water from cells)?
Conductive systems - facilitated diffusion of K and Cl out of cell (no change in electronegativity), water follows Cotransport systems - H/K exchanger and cl/HCO3- exchanger lead to H + HCO3 = H2CO3 -> CO2 + H2O leave cell - K/Cl cotransport out of cell, water follows
26
What mechanisms resist cell shrinking (add water to cells)?
Conductive systems - facilitated influx of Na or Ca, water follows Cotransport systems - influx of H2O and CO2 formation of H2CO3 which forms H (leaves cell, Na enters) and HCO3- (leaves cell, cl enters) - Na/Cl cotransport into cell, water follows
27
In an average human (70kg), how much of the body is water?
60% water 60% of 70 = 42 L water
28
How much of the body's water is extracellular?
1/3 of the body's water is extracellular (2/3 intracellular) So in a 70kg person, 42 L of water - 14 L extracellular - 28 L intracellular
29
Of the extracellular water, how much is interstitial and how much is in plasma?
In a 70kg individual, 14L extracellular water 11L interstitial water 3L plasma
30
What is the circulating blood volume of a 70kg individual?
5L circulating blood volume - 3L plasma - 2L red cells
31
What are the consequences of an increase in the permeability of blood capillaries to plasma proteins?
Plasma proteins leave capillaries which lowers oncotic pressure in the capillaries, enters interstitial space, increases hydrostatic pressure, water follows causes odema
32
What are the glucose transporters on the intestinal epithelial cells?
On the lumen face of the epithelial cells - Na/glucose symporter (uses Na gradient, to transport glucose from intestine into cells) Between epithelial cell and capillary, GLUT2 which transports glucose out of cells into capillaries
33
Where in the body are Na/glucose symporters found?
Intestinal cells | Kidney epithelial cells
34
What glucose transporter is present in adipose, brain, liver and skeletal cells?
Have an insulin receptor that upon insulin binding, causes insertion of glucose channels into the plasma membrane (via exocytosis of vesicles containing channels) allows glucose influx into cells
35
How is glucose that enters cells prevented from leaving?
Converted into either glycogen (storage) or G6P (respiration - glycolysis)
36
What other organic molecules use Na gradient for transport unfavourably up gradient?
Vitamin C | Amino acids